Electrical Induction Device for High-Voltage Applications

ABSTRACT

An electrical induction device for high voltage applications, of the type comprising a magnetic core which has at least one leg ( 1 ) and is operatively coupled to a supporting structure, at least one inner winding ( 10 ) which is arranged around said leg ( 1 ) and has a first rated voltage, at least one outer winding ( 20 ) which is arranged around said at least one inner winding ( 10 ) and has a second rated voltage; and electrically insulating means, characterized in that said at least one inner winding ( 10 ) comprises a plurality of substantially concentric turns ( 11 ) formed by a sheet of electrically conducting material which is spirally wound, and in that said electrically insulating means comprise at least one layer ( 12 ) of electrically insulating material which is arranged between mutually facing surfaces of said concentric turns ( 11 ), and first shaped insulating means ( 4, 5 ) which edge, at least partially, at least one of the upper and lower external rims ( 13,14 ) of said inner winding ( 10 ).

The present invention relates to an electrical induction device for highvoltage applications, in particular an industrial power transformer,having improved performances and an optimised structure.

It is widely known in the art the use of electrical induction devices,such as reactors or transformers, which exploit the electromagneticinduction for properly transmitting and distributing electricity overpower lines.

In particular, the basic task of a power transformer is to allowexchanging electric energy between two or more electrical systems ofusually different voltages. Most common power transformers generallycomprise a magnetic core composed by one or more legs or limbs connectedby yokes which together form one or more core windows; for each phase,around the legs there are arranged a number of windings, i.e.low-voltage windings, high-voltage windings, control or regulationwindings. The phase windings are usually realized by winding around thecorresponding leg of the core suitable conductors, for example wires, orcables, or strips, so as to achieve the desired number of turns; typicalconstructive configurations are for example the so-called multilayer ordisc configurations, wherein the conductors are wound around acylindrical tube which represents an optimal configuration as regard tofilling the area available with useful material and providing also themaximum short circuit strength.

Due to the intrinsic structural characteristics and functioning of thesedevices, a very important aspect concerns the electrical insulationwhich must be guaranteed among the various elements in order to providethe desired electromagnetic performance without incurring in anymalfunctioning or damages, and meet at the same time internationalstandards and regulations; in fact, when these devices are inoperations, there may be a significant difference of voltage among thevarious parts, for example between the low and high voltage windings,among the turns of each single winding, or among the windings/turns andother live/conducting parts such as the tie-rods or clamps of thestructure which is used to support mechanically the electromagneticequipment. Hence, the various components should be arranged with arelative distance determined by the dielectric stress which may beallowed to occur, which requirement is obtained in most cases byadopting particularly devised insulating systems and/or by usingsuitable conductors or configurations for the windings.

Such requirements become more demanding and severe to be satisfied whenincreasing the performance required, for example with induction devicesof the type of the present invention, which are called to provide powerof the order of several tens MVA and have phase windings rated in therange from few kV up to more 100 kV.

At the current state of the art, although the solutions adopted allowachieving appreciable results, there are still some aspects which can beoptimised and technically improved, in particular as regard to theconstruction of the phase windings and the layout of the electricalinsulation, which have a decisive impact over the whole costs andperformance of these devices.

The same considerations apply to a certain extent in most types ofreactors which are basically required to compensate possible variationsof tension over the lines and deal more or less with the samerequirements and problems of power transformers.

Hence, the aim of the present invention is to provide an electricalinduction device for high voltage applications, and in particular anindustrial power transformer, whose constructive structure is optmizedwith respect to equivalent types of known induction devices, and inparticular which allows optimising the manufacturing costs in comparisonwith known devices having the same or comparable power ratings, whileassuring the needed safety and reliability in operations.

This aim is achieved by an electrical induction device for high voltageapplications, of the type comprising:

-   -   a magnetic core having at least one leg and operatively coupled        to a supporting structure;    -   at least one inner winding which is arranged around said leg and        has a first rated voltage;    -   at least one outer winding which is arranged around said at        least one inner winding and has a second rated voltage; and    -   electrically insulating means; characterized in that said at        least one inner winding comprises a plurality of substantially        concentric turns formed by a sheet of electrically conducting        material which is spirally wound, and in that said electrically        insulating means comprise at least one layer of electrically        insulating material which is arranged between mutually facing        surfaces of said concentric turns, and first shaped insulating        means which edge, at least partially, at least one of the upper        and lower external rims of said inner winding. Further        characteristics and advantages of the present invention will        become apparent from the description of some embodiments of the        subject electrical induction device which will be described by        making reference to a preferred embodiment as a three-phase        industrial power transformer, without intending to limit in any        way its possible field of application, and illustrated only by        way of non-limitative examples in the accompanying drawings,        wherein:

FIG. 1 is perspective view of a three-phase power transformer accordingto the present invention;

FIG. 2 is a top plan view schematically showing the inner and outerphase windings of the transformer of FIG. 1;

FIG. 3 is a lateral cross-section schematically illustrating the innerwinding coupled to electrically insulating means according to apreferred embodiment of the device according to the invention;

FIG. 4 is a cross section taken along the plane B-B of FIG. 1,illustrating a tie-rod coupled to electrically insulating meansaccording to a preferred embodiment of the device according to theinvention.

With reference to the above cited figures, the high-voltage inductiondevice according to the invention comprises a magnetic core which isoperatively coupled to a supporting structure and has at least one leg1; in particular, in the embodiment of FIG. 1, the magnetic corecomprises one leg 1 for each phase, namely three, with the legs 1mutually connected by yokes (not visible in the figures) according toconstructive configurations which are well known in the art andtherefore will not be described herein in details. In turn, thesupporting structure comprises a couple of clamps 2 which are positionedon the opposite sides of the core and are connected by one or morevertical connecting elements 3, typically tie-rods.

As shown in FIG. 1, around a leg 1 there is arranged at least one innerwinding 10 which has a first rated voltage, and at least one outerwinding 20 which is arranged around the inner winding 10 and has asecond rated voltage, preferably higher than said first rated voltage;for example, the rated voltage of the inner winding 10 can be 36 kV,while the rated voltage of the outer winding 20 can be 170 kV. Althoughinternational standards generally define the field of low-voltageapplications as that with voltage levels up to 1 kV, and the field ofhigh-voltage application the one with voltage levels above 1 kV, in thetechnical field of induction devices of the type of the presentinvention, the outer winding 20 is normally indicated as thehigh-voltage-winding, whilst the inner winding 10 is usually indicatedas the low-voltage winding (in some cases also as the medium-voltagewinding), and these definitions will be used in the followingdescription.

The induction device further comprises insulating means for providingelectrical insulation among its living\conducting parts, in theembodiments and for the purposes that will be described in detailshereinafter.

Advantageously, as schematically illustrated in FIG. 2, the innerwinding 10 comprises a plurality of substantially concentric turns 11which are built-up by a sheet of electrically conducting material, forexample copper or aluminium, which is spirally wound; preferably, theconducting sheet is formed by a single piece which is continuously woundaround a tubular element (not shown in the figures) in such a way thatthe winding 10 has a whole cylindrical configuration, as illustrated inFIG. 1. The inner winding 10 further comprises a plurality of throughchannels 30 which are provided along various circumferences at differentradial distances from the leg 1, and inside which a cooling fluid flows,for example a mineral oil; in particular, each channel 30 extendsbetween two adjacent turns 11 and for the whole vertical length of theturns 11 themselves, substantially parallel to the leg 1; finally, asillustrated in FIG. 1, in correspondence of the first internal turn 11 zand of the last external turn 11 a, there are provided two correspondingelectrical conducting elements 40, for example bars, which are connectedto and protrude from the inner winding 10 so as to allows its operativeconnection to other components of the device, for example, insulators,other windings, et cetera.

Advantageously, as evidenced in FIG. 3, the electrically insulatingmeans comprise at least one layer 12 of electrically insulating materialwhich is arranged between mutually facing surfaces of consecutive turns11, and first shaped insulating means which edge, at least partially, atleast one of the upper 13 and lower 14 external rims of the innerwinding 10. Preferably, the layer 12 comprises at least one sheet ofcellulose-based material—for example the so-called DDP ordiamond-dot-paper, or other insulating means like polyester-basedmaterial—which is also spirally wound together with the conductivesheet; according to a particularly preferred embodiment illustrated inFIG. 3, the layer 12 comprises two separate sheets 12 a, 12 b, ofcellulose-based material mutually attached to each other and each facinga corresponding surface of a turn 11. In this way, the layer 12 providesan appropriate electrical insulation between each couple of consecutiveturns, and the likelihood of electrical discharges between the turns dueto possible gaps in the insulating layer itself is drastically reducedby adopting two distinct and mutually attached sheets. Preferably, thesheets 12 a, 12 b can be adhered, at least partially to the surfaces ofthe turns 11, thus contributing to increase the structural stiffness ofthe whole inner winding 10.

In turn, as shown in FIGS. 1 and 3, the first shaped insulating meanscomprise a first shaped body 4 and a second shaped body 5 which arepreferably in the form of angular sectors with an L-shaped sidecross-section and are operatively connected, for example by glueing, tothe upper external rim 13 and the lower external rim 14 of the winding10, respectively; as illustrated in detail in FIG. 3, the shaped bodies4 and 5 are positioned with a first side 6 which is positionedsubstantially parallel to the leg 1 and covers a portion of the outersurface 11′ of the last external turn 11 a, and a second side 7 which ispositioned substantially perpendicular to the leg 1 and covers thecorresponding short side 11″ of at least the last external turn 11 a.Preferably, the second side 7 of the first and second angular-shapedbodies 4, 5 has a length L which is shorter than the distance D betweenthe outer surface 11′ of the last external turn 11 a and the externalwall of the most external through channel 30 (with respect to the leg1). In this way, when the bodies 4,5 are coupled to the winding 10, thechannels 30 remain uncovered.

Advantageously, the first shaped insulating means further comprise atleast one U-shaped body 8 which is positioned under the correspondingangular-shaped body 4 or 5, and wraps at least one of the upper or lowertip portions 15 of at least the last external turn 11 a, at least for apart of its whole circumference. Preferably, in the device according tothe invention there are provided a first U-shaped body 8 and a secondU-shaped body 8 which wrap the upper and lower tip portions 15 of thelast external turn 11 a, respectively; more preferably, there are alsoprovided a third U-shaped body 8 and a fourth U-shaped body wrapping theupper and lower tip portions 15 of the penultimate external turn 11 b,respectively, at least for a part of its whole circumference. Accordingto a particularly preferred embodiment, the first shaped insulatingmeans comprise also a fifth U-shaped body 8 and a sixth U-shaped bodywrapping, the upper and lower tip portions 15 of the ante-penultimateexternal turn 11 c, respectively, for at least part of itscircumference. The various U-shaped bodies 8 can be realized by a singlepiece of insulating material, e.g. cellulose-based material such ascrepe-paper, pressboard or other suitable materials; each U-shaped body8 is directly positioned around and embraces the corresponding tipportion 15 for the entire circumference of the respective turn 11 a, 11b, 11 c. Alternatively, such U-shaped bodies 8 can be realized inseveral portions each wrapping a respective part of the correspondingtip portion 15.

In the induction device according to the invention, the electricallyinsulating means preferably comprise also second shaped insulating meanswhich are operatively coupled to and arranged around a portion of atleast one of the electrical conducting elements 40 which are connectedto and protrudes from the inner winding 10. Advantageously, asillustrated in FIGS. 1 and 3, said second shaped insulating meanscomprise a first contoured body 50 having a first L-shaped portion whichis operatively coupled to the inner winding 10—over the U-shaped bodies8 and the L-shaped body 4—with a first side 51 positioned substantiallyparallel to the leg 1 and a second side 52 positioned substantiallyperpendicular to the leg 1; further, the contoured body 50 comprises asecond U-shaped portion 53 which is integral with and rises from thesecond side 52, substantially parallel to the leg 1. The U-shapedportion 53 surrounds, like a collar, at least partially, the portion 42of the conducting elements 40 protruding from the inner winding 10. Inthis way, the body 50, thanks to its particular configuration, allowsimproving the electrical field distribution and hence the dielectricstrength between the elements 40 and the outer high-voltage winding 20.

Preferably, the second shaped insulating means further comprise a secondcontoured body, indicated by the reference number 54 in FIG. 2, which ispositioned at the upper portion of the inner winding 10, preferablysubstantially opposite to the first contoured body 50 with respect tothe leg 1, so as to cover a region of the winding 10 which faces thewinding legs of the outer winding 20, schematically indicated by thereference number 41 in FIG. 2. The second body 54 is preferably in theform of an angular sector with an L-shaped side cross-section, similarto the first L-shaped portion of the contoured body 50; the second body54 is positioned over the first angular body 4 and the U-shaped bodies8, with a first side which is positioned substantially parallel to theleg 1 and covers a portion of the outer surface 11′ of the last externalturn 11 a, and a second side which is positioned substantiallyperpendicular to said leg 1 and preferably extends up to the mostinternal turn 11 z, as schematically shown in FIG. 2.

According to a particularly preferred embodiment, the electricallyinsulating means comprise third shaped insulating means which arearranged around at least a portion of at least one tie-rod 3;preferably, the third shaped insulating means are arranged around alltie-rods 3 and for their whole length comprised between the clamps 2.

Advantageously, as illustrated in FIG. 4, the third shaped insulatingmeans comprise a first layer 60 and a second layer 61 of cellulose-basedmaterial which are tubularly wound around a corresponding tie-rod 3spaced apart from each other, and a third element 62 made of insulatingmaterial which is arranged therebetween; preferably, the first layer 60comprises a sheet of crepe-paper having a thickness ranging between 0.8and 1.2 mm which is placed directly around the tie-rod 3; the secondlayer 61 comprise a sheet of crepe-paper having a thickness rangingbetween 1 and 3 mm which is placed spaced from the first layer 60 so asto define a channel 63 therebetween; in turn, the third element 62 isrealized by a suitably contoured body, for example made of cellulosebased material or wood, which is positioned inside the channel 62 andmutually spaces out said first and second layers 61 and 62.

In this way, a further improved insulation is provided between thetie-rods 3 and the outer winding 20, with also the possibility ofcooling, for example by means of a suitable oil flowing inside thechannel.

In practice, it has been found that the electrical induction deviceaccording to the invention fully achieves the intended aim giving somesignificant advantages and improvements with respect to known inductiondevices. In fact, among the others, thanks to the purposive constructionof the inner winding 10 and the described layout of the electricallyinsulating means adopted, the manufacturing costs can be reduced of asubstantial amount with respect to known types of devices with innerwindings of more conventional construction, while the dielectriccharacteristics among the various parts are substantially improved,according to a solution which is extremely simple in construction andfunctionally effective; thus, it follows that the device of the presentinvention is cheaper with respect to known devices of same ratings andperformances, or it has improved performances, in particular as regardsto the power rating which is of the order or several MVA when comparedto known device of similar cost. The electrical induction device thusconceived is susceptible of numerous modifications and variations, allof which are within the scope of the inventive concept as defined in theclaims; for example, for each phase there might be provided two innerlow-voltage windings 10 which are positioned around the correspondingphase leg 1 spaced apart from and operatively coupled to each other,with the outer winding 20 placed around them, as illustrated in dottedlines only for the central phase in FIG. 1. In this case the secondinner winding 10 has exactly the same construction as the one previouslydescribed with two corresponding bodies 4 and 5 covering its externalrims, and corresponding U-shaped bodies 8 embracing the relative tipportions of only its last turn, or preferably of its last two turns, ormore preferably of its last three turns. Likewise, at the external endof the second winding 10 (the lowest end in FIG. 1), there are arrangedrelative bodies 50 and 54 in the same configuration and for the samepurposes as above described. In turn, there could be only one outerwinding 20 (or two or even several) which is built-up according to amore conventional construction, namely by means or cable, or wires, orstrip arranged in a disc- or a multilayer-configuration.

Finally, all the details may furthermore be replaced with othertechnically equivalent elements, and the materials and dimensions may beany according to requirements and to the state of the art, provided theyare compatible with the scope of and functioning in the application.

1. An electrical induction device for high voltage applications,comprising: a magnetic core having at least one leg and operativelycoupled to a supporting structure; at least one inner winding which isarranged around said leg and has a first rated voltage; at least oneouter winding which is arranged around said at least one inner windingand has a second rated voltage; and electrically insulating means;wherein said at least one inner winding comprises a plurality ofsubstantially concentric turns formed by a sheet of electricallyconducting material which is spirally wound, and in that wherein saidelectrically insulating means comprise at least one layer ofelectrically insulating material which is arranged between mutuallyfacing surfaces of said concentric turns, and first shaped insulatingmeans which edge, at least partially, at least one of the upper andlower external rims of said at least one inner winding.
 2. Theelectrical induction device according to claim 1 wherein said at leastone inner winding has a first rated voltage which is lower than thesecond rated voltage of said outer winding.
 3. The electrical inductiondevice according to claim 1 wherein said first shaped insulating meanscomprise a first shaped body and a second shaped body having an L-shapedcross section, said first and second shaped bodies being connected tosaid upper and lower external rims, respectively, with a first sidewhich is positioned substantially parallel to said leg and covers aportion of the outer surface of the last external turn, and a secondside which is positioned substantially perpendicular to said leg andcovers the corresponding short side of at least said last external turn.4. The electrical induction device according to claim 3 wherein said atleast one inner winding comprises a plurality of through channels eachextending substantially parallel to said leg between two adjacent turns,the second side of said first and second shaped bodies having a length(L) which is shorter than the distance (D) between the outer surface ofsaid last turn (11 a) and the external wall of the most external throughchannel.
 5. The electrical induction device according to claim 1 whereinsaid first shaped insulating means comprise a U-shaped body which wraps,at least partially, at least one of the upper or lower tip portions ofat least the last external turn.
 6. The electrical induction deviceaccording to claim 5 wherein said first shaped insulating means comprisea first and a second U-shaped bodies wrapping, at least partially, theupper and lower tip portions of the last external turn, respectively. 7.The electrical induction device according to claim 6 wherein said firstshaped insulating means comprise a third and a fourth U-shaped bodieswrapping, at least partially, the upper and lower tip portions of thepenultimate external turn, respectively.
 8. The electrical inductiondevice according to claim 7 wherein said first shaped insulating meanscomprise a fifth and sixth U-shaped bodies wrapping, at least partially,the upper and lower tip portions of the ante-penultimate external turn,respectively.
 9. The electrical induction device according to claim 1wherein said electrically insulating means comprise second shapedinsulating means which are operatively coupled to and arranged around aportion of at least one electrical conducting element which is connectedto and protrudes from said at least one inner winding.
 10. Theelectrical induction device according to claim 9 wherein said secondshaped insulating means comprise a first contoured body having a firstL-shaped portion which is coupled to said at least one inner windingwith a first side positioned substantially parallel to said leg and asecond side positioned substantially perpendicular to said leg, and asecond U-shaped portion rising from said second side of the L-shapedportion, which surrounds, at least partially, the portion of theconducting element which is connected to the inner winding.
 11. Theelectrical induction device according to claim 10, wherein said secondshaped insulating means comprise a second contoured body which ispositioned at the upper portion of said at least one inner winding so asto cover a region thereof.
 12. The electrical induction device accordingto claim 11, wherein said second contoured body has an angular sectorconfiguration with an L-shaped side cross-section and is positioned atthe upper portion of said at least one inner winding with a first sidewhich is arranged substantially parallel to said leg and covers aportion of the outer surface of the last external turn, and a secondside which is positioned substantially perpendicular to said leg andextends up to the most internal turn.
 13. The electrical inductiondevice according to claim 9 wherein said supporting structure comprisesa plurality of tie rods, and said electrically insulating means comprisethird shaped insulating means which are arranged around at least aportion of at least one tie-rod.
 14. The electrical induction deviceaccording to claim 13, wherein said third shaped insulating meanscomprise a first and a second layers of cellulose-based material whichare tubularly wound around said tie-rod spaced apart from each other,and a third element made of insulating material which is arrangedtherebetween.
 15. The electrical induction device according to claim 14,wherein said first layer comprises a sheet of crepe-paper having athickness ranging between 0.8. and 1.2 mm which is placed around saidtie-rod, said second layer comprise a sheet of crepe-paper having athickness ranging between 1 and 3 mm which is placed spaced from saidfirst layer so as to define a channel there between, and said thirdelement comprises a contoured body which is positioned inside saidchannel and mutually spaces out said first and second layers.
 16. Theelectrical induction device according to claim 1 wherein said layer ofelectrically insulating material comprises two sheets of cellulose-basedmaterial mutually attached to each other.